The proposed work seeks to elucidate which complement components are synthesized by lymphocytes and monocytes/macrophages and whether any of the components are expressed on the surface of these cells. It will further be investigated whether synthesis can be modulated by cellular products (lymphokines and whether any of the complement components plays a role in cell-cell interaction phenomena (activation). The way in which activated Factor B of the properdin system leads to rapid spreading of human monocytes will be studied and the possible role of Factor B and its mode of activation in other reactions leading to macrophage activation will be analyzed.